This invention relates to a method of processing meat to provide a product having improved microbial stability. More particularly, the invention relates to a method of producing a commercially sterile meat-containing product which is heat processed under conditions which do not adversely affect the flavor, texture, color or appearance of the meat or other ingredients of the product.
Canned low acid foods which are commercially available, generally are heat processed by retorting to prevent microbiological spoilage so that the product, at room temperature, will remain unspoiled indefinitely from a microbiological standpoint. Such canned foods are heat processed to render the product "commercially sterile," which term is defined to mean that degree of sterility at which all pathogenic and toxinforming organisms have been destroyed, as well as other more resistant types which, if present, could grow in the product and produce spoilage under normal storage conditions.
The problems of meat canners in producing sterile canned meat products are often more acute than with producers of other products in the commercial canning industry because meat products are low-acid foods, that is, they have pH of 5.3 and above. It is well known that the heat processing conditions required to produce a commercially sterile product are, in part, dependent upon the acidity of the food being processed. Thus, it is recognized that foods having a pH of 4.6 or below may be heat processed under relatively mild conditions to provide a sterile canned product, since acid-tolerant organisms can, in practically all cases, be destroyed by subjecting acid foods or high acid foods to a short heat process at about 212.degree. F. However, the growth of some microorganisms, such as Clostridium botulinum, is inhibited only in foods having a pH of 4.6 or below and are a health hazard in foods having a pH of above 4.6, including meat and meat products. Such foods having a pH of above 4.6 require high heat processing temperatures for extended periods of time in order that all viable microorganisms are destroyed or rendered dormant. Thus, canned foods having a pH of above 4.6 must be given a minimum safe cook, which for practical purposes is considered to be one having a F.sub.0 of 2.78, that is, is equal in destructive effect on Clostridium botulinum to 2.78 minutes at 250.degree. F., assuming instantaneous heating and cooling. However, such severe heat treatment often results in noticeable changes in flavor, texture and color of meat products.
Several alternative techniques have been suggested heretofore for the production of commercially sterile meat products without subjecting the meat to severe thermal processing. For example, U.S. Pat. No. 3,886,296 discloses subjecting particulate low acid foods to an acid blanch for a period of time sufficient to reduce the overall pH of the food to below 5.0 and then immersing the acid blanced food particles in an acidic liquid phase, such as a sauce or gravy, having a pH of below 4.5, in a suitable container. Due to the acid blanching of the food and the fact that the food is surrounded in the container by an acidic liquid phase, the food particles in the container have an overall pH of 4.6 or below within about 30 minutes, so that the food particles may be heat processed at relatively low temperatures for short periods of time. While this procedure is effective in reducing the thermal processing required to produce a commercially sterile product, it is subject to some disadvantages which tend to limit the use of this procedure in the production of sterile canned meat products. For example, such acidification of meat particles is a relatively slow process which is limited by the rate of hydronium ion diffusion into the meat and influenced by the size and type of meat. Unless the meat particles are small in size, it is difficult to obtain the uniform distribution of acid throughout the meat which is required to enable the meat to be heat processed under relatively mild conditions. Meat, other than pieces which are relatively small in size, are difficult to acidify by the process, thereby limiting the type of canned meat-containing product which may be produced.